So-called "open-heart" surgical procedures, which include coronary artery bypasses and valve replacements, are among the most commonly performed major operations. These procedures entail splitting the sternum longitudinally and spreading the sternum laterally to provide access to the heart. The latter stages of such procedures include closing and stabilizing the sternum, which is often done by means of wire sutures installed trans-sternally (i.e. through the sternum).
FIG. 1 somewhat schematically illustrates the conventional closure procedure using transsternal sutures. As seen in FIG. 1, split-halves 20 and 22 of the sternum are joined together by a series of wire suture loops 24 spaced at intervals in the longitudinal direction relative to the sternum.
When the quality of the sternal bone is poor, due to osteoporosis or other factors, the wire suture may cut into the split-halves of the sternum as the free ends of the wire sutures are twisted together to draw the sternum together.
FIG. 2 is a view which shows the sternum and one of the suture loops 24 in cross-section. The arrows shown in FIG. 2 indicate the main force vectors which result from twisting the ends of the suture. Most of the tension resulting from the twisting procedure is applied at the anterior surface 26 of the sternum, and particularly at the inner edge 28 of the anterior outlets 30 through which the loop 24 emerges from the bone. If the anterior cortex of the bone is of poor quality, the anterior outlet 30 is cut in an inward direction (i.e. toward the sternotomy and the location where the wire ends are twisted together). Consequently, the wire loop 24 assumes an acute angle configuration at the posterior side of the sternum, as indicated at 32 in FIG. 2. Coughing or other post-operative activity may then cause the acute angles 32 of the wire loop 24 to cut the bone in an inward direction at the posterior side of the sternum, leading to dehiscence (separation) of the sternal halves, as illustrated in FIGS. 3 and 4. Serious complications, including infection, may result from sternal dehiscence.
The problem of sternal dehiscence after closure using suture loops is known to the prior art, and various solutions have been proposed. Among these are reinforcement of the sternum by implantation of longitudinally extending wires, or weaving reinforcement wires around the ribs adjacent to the sternum and then applying sutures peri-sternally (laterally around the sternum) to join the sternal halves. However, these proposed solutions tend to result in increased damage to blood vessels or other soft tissue, and also may substantially increase the time required for closing the chest. Also, if infection occurs, necessitating removal of the sutures, it can be very difficult to remove the reinforcing wires.
Another difficulty encountered in closing the sternum by transsternal sutures is the uncertainty as to whether the suture loops have been tightened to an optimum degree. If the loops are insufficiently tightened, then sternal dehiscence may immediately occur. But if the tightening is excessive, the sternal halves may be cut by the suture, as described above, which also can lead to dehiscence. Because of variations from patient to patient in the mechanical properties of the bone, it is not possible to determine the correct degree of suture loop tension by observing deformation of the bone.